When sex researchers compare men and women’s genital arousal in response to various stimuli, they generally find that men tend only to be aroused by stimuli that match their declared sexual preferences and subjective feelings, whereas women tend to be aroused by a broad array of sexual material (including scenes involving chimps), irrespective of their declared preferences and subjective feelings. A new study by Kelly Suschinsky and Martin Lalumiere tests the claim, which will surely prove controversial, that this pattern of responding in women is an evolutionary vestige which served in the past to protect women from the genital injury that can come from unwanted sex.

‘Substantial ethnographic, historical, and comparative evidence suggests that the threat of unwanted sexual activity has been considerable over human evolutionary history,’ the researchers said. Their specific proposal is that women’s indiscriminate genital arousal leads to lubrication which reduces the likelihood of injury occurring when unwanted sexual encounters take place.

To test this claim, Suschinsky and Lalumiere presented 15 heterosexual men and 15 heterosexual women (average age in their early twenties), all currently in a sexual relationship, with 14 two-minute audio recordings of various narratives read by a woman from her own perspective. The narratives varied in whether or not a sexual encounter occurred between a man and a woman, whether or not violence took place, and whether or not the activities were consensual.

Consistent with past research, the men’s genital arousal was far more specific, tending to occur most strongly in response to a consensual, non-violent sexual encounter, which was also the scenario they said they found most arousing. By contrast, the women’s genital arousal was far more uniform across all the sexual scenarios. There was one anomaly – their genital arousal to non-consensual, but otherwise nonviolent, sex was lower than for consensual, non-violent sex, but was still significantly higher than their response to neutral scenarios. Like the men, the women’s subjective feeling of arousal was far more targeted, being much higher for the consensual, non-violent scenario than the others. Both sexes reported finding the violent or non-consensual scenarios unpleasant and anxiety provoking.

Suschinsky and Lalumiere said their results support what they call the ‘preparation hypothesis’, adding to past research showing, for example, that some women report experiencing genital lubrication during rape. The researchers acknowledged some limitations in their study. In particular, the scenarios were all told from a woman’s perspective. However, they said that past research had shown men tend to find this narrative perspective particularly arousing, so this methodological imbalance is unlikely to explain the results. The researchers also acknowledged that their sample were young and sexually active, and likely to be fairly sexually liberal given that they’d volunteered for a study of this kind. ‘We recommend that this study be replicated with a larger and more diverse sample,’ they said.

Given the sensitivity of this research topic, and in particular the possibility that its message might be exploited to justify immoral acts, it’s worth heeding the words of Mary Roach in her book Bonk:

‘It is important to remember,’ she writes, that ‘it is the mind that speaks to a woman’s heart, not the vaginal walls… Rape offers a plangent illustration of this fact. I learned in a paper by Roy Levin that rape victims occasionally report having responded physically, even though their emotional state was a mixture of fear, anger and revulsion. … Regardless of the mechanisms that may or may not explain a rape victim’s physical state, a rapist’s defense based upon evidence of arousal has, to quote Levin, “no intrinsic validity and should be disregarded”.’

You handled this controversial research very respectfully, kudos. Though I sincerely doubt, or at least hope, that no-one would think that ANY biological reaction to ANY stimulus justifies an unwarranted deprivation of another's rights. By that flawed logic we could hold murderers innocent because they don't choose to activate the sympathetic nervous system when they commit a crime. Just as male involuntary erection isn't justification for sex against the male's will, female involuntary lubrication isn't justification for sex against the female's will.

That said, I have to echo Eiko's criticisms. With the stated methodological flaws this can only really be counted as preliminary hypothesis testing, not conclusive evidence for anything. I find it very odd that they chose to only have women read the IV texts and then justified this decision by arguing that male arousal is more affected by females reading the text even though it wasn't the male arousal that was the main measured DV relevant to the hypothesis, but female arousal.

Have males read the text and see if female arousal changes. If we've confirmed male arousal is affected by the gender of the reader, perhaps female arousal is too and could be producing an anomaly in female genital lubrication in either condition.

From an applied psychology perspective this research reminds me of an experience when I accompanied a client to a case conference with the representatives of the Sapphire Unit telling us that her claim regarding an experienced rape cannot possibly be justified in view of the medical evidence, which did not reveal she has sustained any physical injuries. For those who do not know, the Sapphire Unit is the UK Police specialist division dealing with victims of rape. They were so convinced of their approach that they did not even allow for a discussion of the hypothesis that the victim might possibly have had a different psychological and moral versus physical reaction to this horrible event.

As much as I can appreciate suggestions to widen up the sample, it might be equally interesting to narrow it down to groups, which may be subject to persistent sexual offences, such as prostitutes forced to work for pimps or women experiencing domestic violence. This is because apart from the suggested “natural” predisposition for the female biological response to a wider spectrum of stimuli, specific groups may have an additional learnt reaction, resulting from the experience of being hurt, if they did not respond on a physical level in a “collaborative” way. Admittedly, this group may be much harder to reach, however, it is the group, which due to the myths prevailing within the investigative forces, have the least chances for ever finding justice, as it was in the case of my client. The UK statistics show that whether the victim is an experienced sex worker, or a single case victim, she has a minimal chance to ever bring her case to the court hearing.

This research could undermine the current paradigm within the UK justice system, based on the assumption that lack of physical injuries equals consensual sex. The development of this research in this direction could not only attract funding from the legislative authorities, but it could also lead to shedding some light into the lives of many misunderstood victims of rape.

From an applied psychology perspective this research reminds me of an experience when I accompanied a client to a case conference with the representatives of the Sapphire Unit telling us that her claim regarding an experienced rape cannot possibly be justified in view of the medical evidence, which did not reveal she had sustained any physical injuries. For those who do not know, the Sapphire Unit is the UK Police specialist division dealing with victims of rape. They were so convinced of their approach that they did not even allow for a discussion of the hypothesis proposing that the victim might possibly have had a different psychological and moral versus physical reaction to this horrible event.

As much as I can appreciate suggestions to widen up the sample, it might be equally interesting to narrow it down to groups, which may be subject to persistent sexual offences, such as prostitutes forced to work for pimps or women experiencing domestic violence. This is because apart from the suggested “natural” predisposition for the female biological response to a wider spectrum of stimuli, specific groups may have an additional learnt reaction, resulting from the experience of being hurt, if they did not respond on a physical level in a “collaborative” way. Admittedly, this group may be much harder to reach, however, it is the group, which due to the myths prevailing within the investigative forces, have the least chances for ever finding justice, as it was in the case of my client. The UK statistics show that whether the victim is an experienced sex worker, or a single case victim, she has a minimal chance to ever bring her case to the court hearing.

This research could undermine the current paradigm within the UK justice system, based on the assumption that lack of physical injuries equals consensual sex. The development of this research in this direction could not only attract funding from the legislative authorities, but it could also lead to bringing some light into the lives of many misunderstood victims of rape.

This study is itself a replication. There have been numerous studies conducted in the past that have tested this hypothesis, and these results are consistent with previous findings. This isn't a one-off or accidental result.

I agree that the handling of this type of research needs to be very sensitive. But, I would like to suggest that this research works against apologistic rape narratives, rather than with them. The story sometimes goes “her body was saying yes even though she was saying no.” This hypothesis, if is true, works against that justification.

It is over 5 years since I was raped, only now have I been able to begin researching why I experienced vaginal lubrication.

I had been drinking heavily and was in an inebriated black out/sleep. I came to as it was happening. The shame and self loathing and inevitable self-blame were compounded by the confusion and disgust that I experienced towards my body's reaction.

Reading this blog has helped me to understand that my physical response was just that – a physical response, possibly as a result of evolutionary programming. It did not make the event less of a violation, in the same way that my 'flirtatious' behviour towards the rapist, who I thought was my friend, earlier in the evening was not an invitation to invade my body when I was passed out in my own home.

Thanks for your research – please try to extend it and make it more robust. When I came to whilst the rapist was in the middle of his attack he said, 'I couldn't help myself' – of course it felt like my fault, I'd led him on hadn't I? My body had said yes to his actions hadn't it? But I had not consented, I did not want to have sex with him or anyone else. It was not the same as drunk sex I'd had in the past where I'd gone along with it even if I didn't really feel like it by that point. It was profoundly different; it was rape and its effects have been real and continue to require recovering from.

Obviously there was no way that this experience was going to be taken seriously by the police. I did call them for advice, this was pre-Sapphire Unit, and they confirmed that there was little point proceeding with formally reporting it. Perhaps this research might inform an enlightened police officer somewhere, which might make a difference to someone who has experienced this traumatising event.

I am grateful that I came across this research, however 'unconvincing' its methodology may be for some people. As a critical, educated woman who faces the difficulty of resolving how my body's reflex fits into the narrative of that nightmare, I am sufficiently persuaded of its validity.